I have had descendant vex chrome in the past, currently on 2 pieces of gear. But it's not in my collection book. Why is this and how do I fix it?
Being on a piece of gear doesn't count for your collection. The shader has to have been in your actual shader inventory since Warmind released for it to be in your collection. Since it's an Eververse shader, your only options are to hope Tess sells it at some point, or delete one of your items that has the shader, which will hopefully return it to your inventory.